1. Field of the Invention
The present invention relates to a suspension control system and more particularly to a suspension control system effective for suppressing a single shock caused by unevenness of the road surface during vehicular running and subsequent vibration of the vehicle body.
2. Description of the Prior Art
Heretofore, as a vehicular suspension control system, there has been known the suspension control system described in Japanese Patent Laid Open No. 166715/86. This conventional suspension control system will now be explained with reference to FIG. 7. It is provided with a front wheel acceleration detecting means M2 for detecting an acceleration of component applied to a front wheel M1 in a direction perpendicular to the road surface; a discriminator means M3 for discriminating whether or not the acceleration detected by the front wheel acceleration detecting means M2 is outside a predetermined range; and a rear wheel suspension characteristic changing means M5 for changing suspension characteristics of a rear wheel M4 once it is judged by the discriminator means M3 that the detected acceleration is outside the predetermined range.
According to the above construction, the acceleration of a component operating in a direction perpendicular to the road surface is detected by the front wheel acceleration detecting means M2, and the degree of a concavity or a convexity of the road surface is judged by the discriminator means M3 on the basis of the detected acceleration. The result of this judgement is transmitted to the rear wheel suspension characteristic changing means M5. At this time, if the concave or the convex parameter is very large and exceeds a predetermined range, the vibration of the rear wheel M4 is dampened or high steerability and stability are ensured by the rear wheel suspension characteristic changing means M5.
The above conventional suspension control system adopts a controlling method in which an obstacle is detected on the basis of only the level of acceleration for controlling the rear wheel in accordance with the detected acceleration level, and then the passing of the rear wheel beyond the obstacle is judged on the basis of a vehicle speed so as to return the damping force to the original level. Accordingly, the fact is that detection of an obstacle is difficult and uncertain. Besides, in the case of periodically repeated obstacles such as, for example, joint portions of the road surface of an expressway, it is required to change the suspension frequently in synchronism with the road surface irrespective of the vehicular body vibration. Consequently, not only it is impossible to surely detect joint portions of the road surface but also dissatisfaction has heretofore been encountered in effectively suppressing the resonance with the vehicle body to soften the shock from the road surface.
Further, even when a vehicular body resonance is caused by frequently repeated obstacles, there is not enough time to bring a damping force to a hard level or harden the suspension. Additionally, with only a signal from an obstacle, it is not sure whether or not the vehicle body is actually undergoing a harmful vibration.